Pick and place machines are generally used to manufacture electronic circuit boards. A blank printed circuit board is usually supplied to the pick and place machine, which then picks electronic components from component feeders, and places such components upon the board. The components are held upon the board temporarily by solder paste, or adhesive until a subsequent step in which the solder paste is melted, or the adhesive is fully cured.
Pick and place machine operation is challenging. Since machine speed corresponds with throughput, the faster the pick and place machine runs, the less costly the manufactured board. Additionally, placement accuracy is extremely important. Many electrical components, such as chip capacitors and chip resistors are relatively small and must be accurately placed on equally small placement locations. Other components, while larger, have a significant number of leads or conductors that are spaced from one another at a relatively fine pitch. Such components must also be accurately placed to ensure that each lead is placed upon the proper pad. Thus, not only must the machine operate extremely fast, but it must also place components extremely accurately.
In order to enhance the quality of board manufacture, fully or partially populated boards are generally inspected after the placement operation(s), both before and after solder reflow, in order to identify components that are improperly placed or missing or any of a variety of errors that may occur. Automatic systems that perform such operation(s) are highly useful in that they help identify component placement problems prior to solder reflow allowing substantially easier rework or identify defective boards after reflow that are candidates for rework. One example of such a system is sold under the trade designation Model KS Flex available from CyberOptics Corporation of Golden Valley, Minnesota. This system can be used to identify such problems as alignment and rotation errors; missing and flipped components; billboards; tombstones; component defects; incorrect polarity; and wrong components. Identification of errors pre-reflow provides a number of advantages. Rework is easier; closed-loop manufacturing control is facilitated; and less work in-process exists between error generation and remedy. While such systems provide highly useful inspection, they do consume plant floor-space as well as programming time maintenance efforts and the like.
One relatively recent attempt to provide the benefits of after-placement inspection located within a pick a place machine itself is disclosed in U.S. Pat. No. 6,317,972 to Asai et al. That reference reports a method for mounting electric components where an image of a mounting location is obtained prior to component placement, and compared with an image of the mounting location after component placement to inspect the placement operation at the component level.
While the state of the art for component placement machines has advanced, such machines still require a relatively significant amount of setup, and operator attention. Often, such operations require the placement machine to be taken offline, thus not producing any product for the duration of the setup or maintenance operation. Accordingly, reducing the duration of such operations can provide a significant improvement in effective throughput of a given machine. Pick-and-place machines require such operations as reprogramming, changes of conveyors, workpiece setup, and feeder exchanges. Advances in the design and assembly of printed circuit boards, in particular, have generated a shift toward high-mix, low-volume (HMLV) manufacturing, which requires a higher frequency of line changeovers.
When a given component feeder is depleted of all components, the feeder is generally exchanged with a new feeder having a new supply of the same components. However, it is possible that the new feeder may have incorrect component values; incorrect component type; and incorrect polarity. Thus, when such a feeder exchange is required, the new feeder and/or components placed therefrom must be carefully analyzed by a technician to assure that the placement process can resume. This technician time consumes labor costs, while simultaneously keeping the machine offline. Accordingly, it is important to minimize the time required to effect any given component feeder exchange.